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Choosing an antenna for your boat

A boat can have many types of antennas for communications, and others for navigation and entertainment.  In each category so there are many types of antennas to choose from.  To complicate matters even more, there are combination antennas that do multiple jobs in one package.  However, the only way to get to the end is to start... somewhere... so let's take a look at the most common antenna need, VHF, first.

A VHF antenna normally broadcasts and receives within the VHF band.  VHF is a method of encoding transmitted signals, but by world accord (isn't that amazing!) certain frequencies and "bands" of frequencies are reserved for maritime VHF communication.  Connected to a transceiver, like Shakespeare's SE 2001-EX, SE 2010, or the unmatched SE 6000TM nav-com, a VHF antenna puts you in touch with your fellow boaters, with drawbridge operators, and if needed with the Coast Guard (or other maritime authority in your country).  VHF systems let you call for help, receive weather information, and exchange necessary communication with fellow boaters.  The range for VHF is not very far - line of sight from the antenna, actually.  For longer range communication other choices abound.

In a VHF system, the antenna is the most important link.  A poor antenna will give poor system performance from even the finest transceiver, and a great antenna will help you get the absolute best out of a marginal transceiver.

  • What boat?
    In choosing an antenna for your boat, the first consideration is the boat itself, as well as what type of boating you do with it.  If yours is a simple fishing boat that would be dwarfed by a 23-foot antenna, then of course the longer, better, higher-gain antennas are out of the question.  If yours is one of the luxurious boats with the multiple decks and the hot and cold running champagne, then that 23-footer might not even do - you might need the longer range communications of SSB and Shakespeare's 35-foot Styles 222 and 229-F antennas.  Or check into Shakespeare's other large VHF Commercial Antennas, instead.  Remember, though, that the important consideration is not just the size of the boat, but what you do with it.  If you never take your 90-footer out of Lake Fishbitten, then you don't need a huge antenna, after all.  And it's not likely that you'll take your bassboat Pacific island hopping.

    If that small fishing boat at the fishing boat store got you hooked, look into Shakespeare's three-foot antennas like the Style 5240-R.  It's a half-wave, Low Profile, end-fed antenna with a 36" stainless steel whip and chrome plated brass ferrule.  The Style 5241-R is the same design as the 5240-R, but with a heavy-duty stainless steel whip for stability at high speeds.  The 5247 is basically the same thing, but its heavy duty whip Lifts and Lays down out of the way while you cast around the boat in search of the elusive bass creature.  If you need to remove your antenna for storage of your boat, the Style 5242, has a quick-disconnect fitting for easy attachment and removal of its stainless steel whip.

    VHF antennas can be mounted on a flat surface, or attached to a rail.  For sailboats, you can mount low-profile antennas like these or the 5215 series on a mast, and the extra height of the mast will give them superior performance.  The Style 5215-C-X even comes with a 60-foot coax for just such mounting.  We'll come to a more thorough treatment of antennas for sailing vessels later on.

    These low-profile antennas are three feet long.  One size larger would be the five-foot Style 396-1.  Remember, with VHF, longer and higher is better.  The smaller antennas might all you need for close-in, however, or your boat might not accommodate a longer antenna.  Can you see one of those 23-footers on a bassboat?  The bass would laugh themselves silly.

  • Consider the available space for mounting an antenna (and a radio), and how the antenna will have to be mounted.
    • Rail mounting.  Antennas attach easily to a variety of sizes of rails with handy rail mounts.  The ratchets on them make lowering the antenna quite easy - for fishing or trailering, whatever.  The rails can be horizontal  or vertical, slanted or not.  The simplest rail mount is Shakespeare's Style 4720 Economy Rail Mount.  It's a simple clamp and a simple 1"-14-thread bracket that holds the antenna to the clamp.
    • Surface (deck or bulkhead) mounting, flat or vertical.  Mounting an an antenna to a flat surface requires either a flange mount, or a ratchet mount.  Larger antennas have their own special needs - discussed shortly.  On most boats, it's a safe bet that most of the available flat surfaces aren't exactly vertical or horizontal.  They slope.  The easiest way is with a ratchet mount that handily adjusts for the sloping surface and still permits quickly raising or lowering the antenna in the direction you want.
    • Mounting Kits.  Even if your boat is large enough so you don't have to take down your antennas to fish, many longer antennas probably have to be lowered to clear bridges, boat houses or other overhead obstructions.  The two-part antenna mounting kit provides that option.  The upper bracket snaps open, so you can lay down the antenna when you need to, and raise it again quickly when clear of the obstacle.
    • Mast mounting (for sailboats, or attached to some mast-like structure on your boat).  Antennas can be strapped to a mast quite easily.  Some antennas are intended for this mounting method, having an elongated sleeve at the bottom for the purpose.
  • Where will it be on the boat?
    Your antenna should definitely be mounted as high as possible.  That's super important, so here it is again:  Your antenna should definitely be mounted as high as possible.  VHF signals are line-of-sight only. so, the higher you can mount your antenna, the farther it can "see" to the horizon, and the more boats or other radios it can reach.

    In this respect, sailboats have it made.  Installation of a small antenna on top of a sailboat's high mast can give performance equal to or better than a long antenna on a small boat.

    Choosing a location for your antenna is an extremely important part of choosing the antenna itself.  Remember to keep the antenna away from large metal objects, and especially away from other radiating devices (like other antennas).  The antenna should not be mounted closer than three feet from the radio, but it shouldn't be so far away that the radio's signal is depleted before it gets to the antenna.

    Don't forget to consider where you have to put the boat when it's not in use.  If the antenna will have to be lowered when you come in to port, you'll have to be able to get to it to do so.
     

  • What kind of boating do you do?
    The real question is:  How much range do you really need from your radio?  The farther you venture from shore the longer reach you'll need from your radio - and thus from your antenna - to communicate with base stations like the Coast Guard.  The farther out you go, the farther you have to reach to communicate with other boats, too.  It can get pretty sparsely populated out there.  If yours is a fishing vessel, and you need to communicate with others in your fleet who are some distance away, you'll need a large antenna, high up.  For VHF, output power is limited to 25 watts.  So, the antenna has to "reach" with its antenna gain, a function of antenna height, length, and quality.
     
  • Safety first
    The main reason people have VHF radios on board is to call for help, if help is ever needed.  So, make sure the system you choose will have enough reach and power to be of service in an emergency.  Simply rapping with the other boaters around your dock is fine, but if you need help, you want to be able to call for help and be heard.  Don't shortchange yourself into a small antenna that won't get your signal across the water when you need it most.  When it comes to safety, err on the side of caution.
     


     
    Here is a formula for calculating the range of an antenna: 

    Calculation for Range of an Antenna: 

    Square Root of Height (in feet) above water x 1.42 = Range in miles 

    Remember to perform the calculation for BOTH vessels, then add the results to get the range between two vessels.

     


     
  • Antenna Gain
    Shakespeare's VHF antennas come in gain categories, like 3dB, 9dB, etc.  This is a measure of how efficient the antenna is with the signal you feed it, but it depends a great deal on the length of the antenna.  The gain of an antenna is stated in deciBels (dB) of effective radiated power.  Gain is an increase (or even a decrease) in ERP.  You do not get antenna gain from any so-called amplifiers built into the antenna, and it does not mean you can put more than the maximum legal 25 watts into a VHF antenna.  You only get dB gain from longer, more efficient antennas.  High gain factors are 6dB, 9dB, and thereabouts.  Unity means no antenna gain - a multiplier of "one."

Shakespeare Marine TV Antennas
 
The world of boating is a wonderful world, indeed, but it only has the comforts of home if you take the comforts along with you.  Take television, for example.  TV signals are, like VHF radio, line-of-sight.  Commercial broadcast stations go to great lengths - up to 2000 feet - to get their antennas as high as possible for the widest coverage, but if you're way down at "sea" level on your boat, you might need a decent TV antenna to pull them in, and get all those wonderful television shows coming in clear on your boat.
 
Shakespeare's marine TV antennas come in two main types: omnidirectional and directional.  Generally, if you're going to do most of your marine TV watching anchored someplace (there are lots of other considerations, too, naturally), you'd go for a directional TV antenna.  These have the same benefits as the ones on top of your house - they can be rotated for best reception of various stations.  That is, you can point them toward a station, and easily re-aim them for a different station if you need to.
 
On the other hand, if you're going to do a lot of TV watching out on the water, where rolling seas and oft-changing course would keep a couple of galley slaves busy re-aiming a directional antenna, you can keep life simpler with an omnidirectional antenna.  It doesn't have to be aimed to pick up the stations.

Shakespeare's directional TV antennas are the SeaWatch® 2040 and the SeaWatch® 2050.  The latter goes the extra mile by adding an infrared remote control with which to aim the antenna.  The 2040 has a cable-tethered remote.

Adjusting for Signal strengths
Another thing about Marine TV is you don't know whether you're going to be watching from dock side, where the stations come in strong, or from after a day of fishing at your favorite spot, where the signals are far from optimal.  Shakespeare's SeaWatch® 2025 Marine TV Antenna, an omnidirectional one, offers a solution:  adjustable signal amplification.  The sleek looking antenna comes with dual amplifiers that let you boost or attenuate the signal as needed, using a knob on the controller panel.  The 2025 also steps out of the way when it's off, switching in its auxiliary input (for cable or satellite TV reception, if you provide the appropriate hardware and program service).
 
 
A little tip from the Technical Support department here: marine TV antennas should not be mounted in your vessel's spreaders.  It's better to mount the antenna above or below the spreaders.

 

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